From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-90333][IMPORTANT] dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream Date: Thu, 17 Sep 2026 15:20:17 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-90333 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 6 X-AL-KERNEL-ActionableScore-Lower: 5 X-AL-KERNEL-Commit: 5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 List-Id: CVE: CVE-2026-90333 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: YES Patch: dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream Commit: 5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333 Analysis date: Thu, 17 Sep 2026 15:20:17 -0400 ActionableScore: 6 ActionableScore lower bound: 5 Actionable bucket: Actionable Moderate / Strong Important candidate requiring manual review Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90333 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: IMPORTANT Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-90333 IMPORTANT https://www.kernelcve.org/list/?q=CVE-2026-90333 CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H';CWE-345;CWE-347;CWE-354;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:L';BEST CVSS score: '7.1';DESCR 'dm-integrity accepted a constant DISCARD_FILLER tag as evidence that a block was discarded and then skipped HMAC verification for that block. An attacker with raw write access to the backing device but without the integrity key could stamp a chosen metadata tag with all 0xf6 bytes and make modified storage content be treated as authentic. For the CVSS the PR:L is used in the paranoid score because the attacker does not need the integrity key but does need practical write access to the lower raw device or an equivalent storage layer position. The issue is not directly network reachable through dm-integrity itself. Impact is an integrity bypass for protected block data, with possible availability impact if trusted data is corrupted or system data is modified.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate / Strong Important candidate requiring manual review (with actual score 6) YES DISK INIT LOG HARDWARE LINUS KPANIC MEMORY KPANIC INCREASED_TO_HIGH_BASED_ON_GUESSCVSS NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=6 ActionableScoreLower=5 PrimitiveClass=CLASS_A RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=NO ImportantCandidate=YES ManualReview=REQUIRED AutoDowngradeAllowed=NO 1. ActionableScore * Raw conservative score: 5 * Conservative score: 5. No floor or cap applied. * Raw paranoid score: 6 * Paranoid score: 6. No floor or cap applied. * Final recommended bucket: **Actionable Moderate / Strong Important candidate requiring manual review**:: 2. Signal breakdown Positive conservative signals: * +2 Security-boundary bypass: dm-integrity treats a constant all 0xf6 DISCARD_FILLER tag as proof of discard state and skips HMAC verification. * +1 Integrity plausible: attacker-controlled block metadata can make modified backing storage content be accepted as authentic without the integrity key. * +1 Practical exploit chain strongly implied: raw backing-device write -> forged discard tag -> HMAC bypass -> unauthenticated data served through dm-integrity. * +1 Important storage integrity path: dm-integrity is specifically a block-layer integrity/authentication mechanism, so bypassing tag validation affects a security-relevant storage boundary. Additional paranoid signal: * +1 Availability plausible: forged authenticated-looking storage content can corrupt trusted data or system data, which may cause device, filesystem, or workload unavailability. Non-awarded or withheld signals: * +0 RealUAF: no UAF, stale pointer, double free, refcount mutation, or lifetime corruption is established. * +0 Memory corruption: this is a cryptographic/authentication logic bypass, not kernel memory corruption. * +0 Remote reachable: no direct network path through dm-integrity is established. * +0 Local unprivileged trigger: ordinary local user reachability is not established. * +0 Confidentiality: the patch supports integrity bypass, not a read/disclosure primitive. * +0 Strong LPE: no privilege escalation, arbitrary write to kernel memory, credential manipulation, or controlled kernel corruption is shown. * +0 Host-admin penalty: raw backing-device write access is required, but host-admin-equivalent privilege is not positively established by the supplied evidence. * +0 Rare subsystem penalty: dm-integrity and allow_discards are configuration dependent, but the prompt requires concrete evidence before subtracting for rarity. 3. Reachability analysis The attacker must have raw write access to the backing device or an equivalent lower storage-layer position, but must not know the dm-integrity HMAC key. This is not ordinary packet-triggered or syscall-only reachability. It is also not shown to be reachable by an unprivileged local user. HostAdminRequired is UNKNOWN because raw backing-device write access often implies high local privilege in ordinary host deployments, but the supplied attacker model can also represent a compromised lower storage layer, storage service, device passthrough, or another actor below the integrity layer. NamespaceScopedPrivilege is NO because the relevant operation is not a namespace-scoped capability path. Prior setup exists in the sense that the dm-integrity target must be configured with the old allow_discards behavior in standalone/internal-hash mode. No special hardware or race is required. 4. Primitive and severity interpretation The primitive is a cryptographic integrity/authentication bypass in dm-integrity discard-tag handling. A stored all 0xf6 tag is semantically reinterpreted as an authentic discarded-block marker, and dm_integrity_rw_tag() skips HMAC verification for that block. This lets an attacker who can write raw backing metadata forge the marker without the key. PrimitiveClass is CLASS_A because the bug defeats a meaningful security boundary: authenticated block integrity. The demonstrated consequence is unauthorized integrity modification of protected block data. The speculative consequence is broader availability impact if critical data is corrupted. ImportantCandidate is YES because this is not a DoS-only bug and not a simple configuration warning. AutoDowngradeAllowed is NO because automatically closing it as ordinary Moderate would lose a concrete storage integrity boundary bypass. Likely operational severity is actionable Moderate at minimum, with Strong Important review warranted depending on deployment exposure of the backing device and the sensitivity of data protected by dm-integrity. 5. One-sentence report phrase dm-integrity allowed a forgeable constant discard tag to bypass HMAC verification, so an attacker with raw backing-device write access but without the integrity key could make modified storage blocks appear authentic. 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a concrete cryptographic storage-integrity boundary bypass with high integrity impact, and deployment-specific exposure of raw backing-device write access determines whether it should be treated as Important. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: dm-integrity: replace forgeable discard filler with a keyed sector marker [ Upstream Commit: 5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 Changed files: drivers/md/dm-integrity.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5c58ea19a909ef6bed4f0f824e9cd7e30d7e4775 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-90333 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90333 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:H The Best / paranoid CVSS score: 7.1 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: 5 Paranoid ActionableScore: 6 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: IMPORTANT KPANIC detected for this report: YES Published priority for this report (same as in Subject): IMPORTANT These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).